The present application claims priority to Application No. 101 58 223.4, filed on Nov. 16, 2001 in the Federal Republic of Germany, which is expressly incorporated herein in its entirety by reference thereto.
The present invention is directed to an angle measuring instrument.
Angle measuring instruments are used to measure both the angle of rotation of a rotating shaft within one rotation, as well as the number of rotations executed by the rotating shaft, so that, by combining the two measuring results, the absolute position of the rotating shaft can be determined even after several rotations have occurred.
For example, a single-turn rotary position transducer is used to measure the angle of rotation of a rotating shaft within one rotation. When configured as a rotary encoder, the transducer allows both an angular measurement to be taken in incremental measuring steps at the rotating shaft, as well as an absolute angle determination to be made within one single shaft rotation.
To determine the number of shaft rotations that have occurred, multiturn rotary encoders are used to determine the absolute angular position within one shaft rotation, i.e., between 0xc2x0 and 360xc2x0, via an encoder disk (a disk containing a coded pattern) which is connected to the shaft and which is scanned with the aid of a suitable photoelectric scanning unit. To obtain the required information regarding the number of effected shaft rotations, typically a reduction or step-down gear is provided, by way of which, with a rotating shaft, the one or more partial disks or encoder disks is/are set into a rotary motion at a low number of revolutions per unit of time, i.e., a slow speed. The rotational movements of the additional encoder disks are likewise measured using one or more photoelectric scanning units, so that, on the basis of the known reduction of the rotary motion of the additional encoders disks, the number of executed shaft rotations can be determined. It is also possible to measure the absolute position of the rotating shaft over a plurality of rotations.
From German Published Patent Application No. 28 17 172, partial disks coupled to gear wheels may be photoelectrically scanned. In this multi-stage incremental shaft encoder, a first encoder disk is provided concentrically to the shaft, and the other succeeding encoder disks are configured in a common plane. The encoder disks are scanned photoelectrically such that the receivers are located on the side of a board facing the encoder disks, and the receivers on another board fixed to the housing.
Since the process of photoelectrically scanning a plurality of partial disks using one photoelectric scanning device, as the case may be, is expensive and susceptible to contamination, such that it can only be carried out under appropriate ambient conditions or by properly encapsulating the measuring device, to reduce the outlay for components, German Published Patent Application No. 196 26 654 describes measuring the rotary motion of gear wheels using strain-sensing elements, which are in a positive contact with the particular gear wheel. In contrast to the spatial configuration of the reduction gear or of the individual gear wheels in a common plane, as described German Published Patent Application No. 28 17 172, in the system illustrated in German Published Patent Application No. 196 26 654, the individual gear wheels are staggered in the axial direction.
It is therefore an object of the present invention to provide an angle measuring instrument of the type set forth at the outset, which will enable the number of executed shaft rotations to be simply determined, which is insensitive to contamination, is suited for simple and high-resolution scanning operations, and which allows a plurality of specific configuration embodiments having different space requirements.
The above and other beneficial objects of the present invention are achieved by providing a measuring instrument as described herein.
An angle measuring instrument according to the present invention includes a simple configuration and a functioning that is insensitive to contamination, which renders possible a plurality of exemplary embodiments having different space requirements, and which is equally suited for a simple as well as for a high-resolution acquisition of the number of executed shaft rotations.
German Published Patent Application No. 197 51 853 describes the principle of inductive scanning for a device for determining the absolute angular position of a rotating shaft within one shaft rotation, i.e., for a pure single-turn rotary position transducer. However, no reference to applying this principle to a multiturn rotary position transducer can be inferred from this publication.
The present invention achieves the objective by starting out from a fundamental consideration that, given a suitable designed multiturn rotary position transducer, the principle of inductive or capacitive scanning may be applied, while attaining the associated advantage of insensitivity to contamination and a rugged, economical type of construction, even in the case of a multiturn rotary position transducer. In particular, a multiturn rotary position transducer which functions in accordance with the inductive or capacitive scanning principle to determine both the absolute angular position of a rotating shaft within one shaft rotation, as well as to determine the number of executed shaft rotations, may be combined with a single-turn rotary position transducer which functions in accordance with the principle of inductive or capacitive scanning.
In the various exemplary embodiments of the approach according in the present invention, the multiturn rotary position transducer, which functions in accordance with the inductive or capacitive scanning principle, may also be combined with any other single-turn rotary position transducers, which work, for example, according to the photoelectric or magneto-resistive scanning principle, without affecting the advantage of a simple design and of insensitivity to contamination of the multiturn rotary position transducer which works in accordance with the inductive or capacitive scanning principle.
The sensor device of the multiturn rotary position transducer, which works according to the inductive or capacitive scanning principle, may include at least one sensor track having at least two sensor windings, which are phase-shifted with respect to one another and which emit phase-offset, periodically modulated sensor signals in response to the relative motion between the scanning device and the graduation structure, while the device for generating an electromagnetic excitation field has exciter elements positioned on both sides of the sensor track which produce the most homogeneous possible electromagnetic field in the region of the sensor track.
The exciter elements may include a current-carrying conductive track or of a plurality of current-carrying conductive tracks disposed in parallel to one another, the conductive tracks of the exciter elements being interconnected such that the current flow is oriented in opposite directions in the conductive tracks positioned on both sides of the sensor track. In this context, the graduation structure may be placed on a circular graduation board and include a first, circularly formed graduation track, made up of an electrically conductive circular segment and an electrically non-conductive circular segment. The scanning device may include a scanning structure which is positioned on a circular scanning board and may have a sensor device which has the sensor track assigned to the graduation track, the sensor windings of the sensor track allowing an absolute positional determination over the detectable measuring range.
At least one graduation and one inductive scanning, including a sine and cosine graduation track, may be assigned to each gear unit, so that the angular information relevant to the gear unit in question may be acquired for each gear unit by performing an arctan calculation.
To increase accuracy, the graduation indicative of a shaft rotation may also have assigned to it a fine graduation in the form of an incremental graduation track, in that the graduation structure is provided with a second circularly formed graduation track, which is radially adjacent to the first graduation track and is formed as a periodic sequence of a plurality of electrically conductive graduation regions and electrically non-conductive graduation regions, the corresponding scanning device having a scanning structure, which has a sensor device having a second sensor track 80 (FIG. 2) which is assigned to the second graduation track 41 and in which sensor windings SWC, SWD (FIG. 2) are arranged to enable an additional, incremental positional determination.
A divided circle-shaped graduation structure is formed on a copper-coated graduation board, a structurally patterned metal disk, or on a partially metallized plastic part, in particular on a metallized gear wheel.
The device for determining the absolute angular position of a rotating shaft within one shaft rotation includes a detecting device having a graduation structure positioned on a graduation board and a scanning device mounted on a scanning board for transmitting output signals which are dependent upon the absolute angular position of the rotating shaft within one shaft rotation. The output signals of the device for determining the absolute angular position of the rotating shaft within one shaft rotation and the sensor signals of the device for determining the number of executed shaft rotations are transmitted to an evaluation unit.
The graduation and scanning device of the single-turn rotary position transducer, i.e., the device for determining the absolute angular position of a rotating shaft within one shaft rotation, and the evaluation board of the evaluation unit are positioned coaxially with respect to the shaft. However, the graduation and scanning devices of the single-turn rotary position transducer and of the multiturn rotary position transducer may be axially allocated in a different manner.
In a first exemplary embodiment, the graduation and the scanning devices of the single-turn rotary position transducer may be positioned on one side of the evaluation unit, and the graduation and scanning devices of the multiturn rotary position transducer on the other side of the evaluation unit, while in a second exemplary embodiment, the scanning device of the single-turn rotary position transducer and the scanning device of the multiturn rotary position transducer are positioned on both sides of a common scanning board, opposite the corresponding graduation devices assigned to the scanning devices.
In another exemplary embodiment, where a scanning board common to the single-turn rotary position transducer and the multiturn rotary position transducer supports the multiturn scanning on one side and the single-turn scanning, on the other side, only a one-time contacting between the evaluation board and the common scanning board is necessary, so that the requirements for an inexpensive angle measuring instrument are met.
Instead of configuring the graduation and scanning structures on printed-circuit boards or boards, the graduation structure may be placed on the peripheral surface of a cylindrical member and have a first graduation track made up of an electrically conductive and an electrically non-conductive peripheral cylinder section, while the scanning device has a scanning structure which is placed on a cylindrical housing and which has a sensor device having a sensor track which is assigned to the graduation structure and which has sensor windings wound on the peripheral cylinder surface which are configured to enable an absolute positional determination over the detectable measuring range.
In this exemplary embodiment, the graduation structure may have a second graduation track which is axially adjacent to the first graduation track and which is formed as a periodic sequence of a plurality of electrically conductive graduations regions and electrically non-conductive graduation regions, and the scanning device may include a scanning structure which is positioned on the cylindrical housing and which has a sensor device having a second sensor track 80 (FIG. 2), which is assigned to the graduation structure and which has sensor windings EW3 (FIG. 2) wound on the peripheral cylinder track surface which are configured to enable an additional incremental positional determination via sensor windings SWC, SWD. The windings may be applied in a spatial form directly in a plastic gear housing, and the graduation may be configured in a planar or cylindrical form. In particular, the windings may be placed on a flexible conductor which is secured, for example by bonding, to the peripheral surface of the cylindrical housing, radially encircling the same.
In so-called drum divisions, the scanning is no longer sensitive to changes in the distance between the graduation device and the scanning device.
The graduation structure may be formed on a copper-coated cylindrical member, a structurally patterned metal cylinder, or on the surface or peripheral area of a partially metallized plastic part, in particular on a metallized gear wheel.
The dimensional example embodiment of the graduation structure may be fabricated using the two-component injection-molding process, the injection-molding process including inserts, or by coating a substructure. Alternatively, the dimensional embodiment may be formed on a substructure completely made of metal or of a conductive plastic, the division being formed by height gradations, recesses, holes, etc.
The device for determining the number of executed shaft rotations may have a plurality of gear units for the defined reduction of the rotational movements of the shaft, the exciter elements of the multiturn rotary position transducer receiving the excitation signals which are assigned to the gear units and which are modulated to a carrier frequency, while the exciter elements of the single-turn rotary position transducer are fed excitation signals which are modulated to a carrier frequency which differs by a predefinable frequency difference from the carrier frequency that is applied to the exciter elements of the multiturn rotary position transducer.
The exciter elements may be assigned to the gear units which are fed by a common exciter resonant circuit.
By selecting different carrier frequencies for the single-turn rotary position transducer and the multiturn rotary position transducer, an unwanted mutual influencing of the excitation coils is prevented. The difference between the carrier frequencies may be such that the mutual influences are negligible following a band-pass filtering.
Instead of one evaluation unit for each gear unit, the scanning devices of the individual gear units may be connected via a multiplex device to a common evaluation unit, so that the multiturn scanning devices assigned to the individual gear units are evaluated one after another via the multiplex device, by the same electronics.
In particular, two high-frequency modulated sensor signals, which are 90xc2x0 out-of-phase, may be amplified, filtered, and demodulated by the multiturn scanning devices assigned to the gear units, and the resulting low-frequency sensor signals may be amplified and sent via an analog/digital converter to a device for calculating positional values, which sends an encoded output signal to a display device and/or follow-up electronics.
To achieve sufficiently accurate sensor signals, in place of a fine signal adjustment in the device for calculating positional values, an adjustment may be undertaken using a table of correction values. Here it suffices to have a table of correction values which may be stored in a memory chip and be taken into consideration when the angle calculations are made for the particular gear unit.
In addition, it is possible for the evaluation unit of the single-turn and multiturn rotary position transducer to be integrated in an application-specific, integrated circuit (ASIC). By properly configuring the relevant interfaces, the multiturn rotary position transducer based on the inductive scanning principle may be optionally combined with an optical, magnetic or inductive single-turn rotary position transducer.